Studies are being carried out on the mechanism of action of nerve growth factor. The major experimental tool used are cultures of PC12 rat pheochromocytoma cells and cultured rat sympathetic neurons. Among questions being investigated are the fate of NGF within its target cells, the selection and exploitation of cells that are mutant with respect to their NGF response, the role of both transcriptional and of non-transcriptional steps in neurite outgrowth, the effect of NGF on the cell cytoskeleton and the effect of NGF on the cell surface architecture of its target cells.